Add TaskProgress and TaskPlan chat components

[pglevy]

Ports TaskProgress and TaskPlan from propeller to sailwind.

Changes

• TaskProgress — collapsible task checklist with progress bar (uses sailwind ProgressBar)
• TaskPlan — collapsible task plan with object type icons, read-only and editable modes (uses TextField, ParagraphField, DropdownField)
• Sorted chat barrel exports and Storybook sidebar alphabetically
• Stories for both components

Notes

• SAIL-style UPPERCASE status values
• Accessible: aria-expanded, role=list/listitem, sr-only status labels, labeled progress bar
• Bumped muted text to gray-600 for contrast compliance

[pglevy]

One state-synchronization issue to consider in TaskPlan:

openItems is initialized from tasks only when the component mounts. If tasks are loaded asynchronously or new tasks are added later, their IDs are never added to openItems, so those tasks start collapsed even though tasks present at mount default to expanded.

Consider synchronizing newly introduced task IDs into openItems, or exposing an explicit expansion policy/default so prop updates behave consistently.